Conventional carburetors are equipments that mix the proportional gasoline with air in a vacuum condition generated by an engine so as to supply mixed gas to the engine. A conventional carburetor includes a throat, a jet pipe and a floater chamber for storing gasoline from the gasoline tank. The throat shaped as a wasp waist has two wider end openings and a narrow middle portion, therein one end opening is connected with the air, and the other end opening is connected with the engine, so that the gasoline is jetted from the jet pipe to achieve the mixture between gasoline and air. However, the conventional carburetor can only achieve mixture between gasoline and air, but can not mix gas such as natural gas (NG) with air. In other words, it's unachievable to use multiple gases for the engine, which is inconvenient.